2012-2013 Winter Prediction

At this point, I would be lying if I said I was completely confident in what this upcoming winter is going to do. After getting hosed for last winter's forecast (the snowy start turned out to be a very warm, wet start), I have learned a great deal more to what is entailed with long term climate predictions. Indeed, about the only thing I got right last winter was the "high precipitation, active storm track" part.

But another year has passed and I spent the better part of that year with some of the most gifted minds at NC State University. I learned of new indices, new techniques, and more importantly, got a better understanding of the working mechanics of the atmosphere. The past year was a year well spent.

We have several indices which can be tracked on a longer term scale than others. These longer (6-month to multi-year time scale) anomalies paint a very fuzzy image of what this winter will bring for us. Then we have shorter term anomalies which act as the wild cards for how our winter will progress. Basically, these longer term anomalies are like the tide on the beach while the shorter term anomalies are like each individual wave crashing onshore.

I don't mean to have such a long prelude, but there is much to look at with such a winter forecast. Please, fasten your seatbelts for "L'Heureux's Winter Forecast" ride and keep your arms and legs in the vehicle at all times.

I will be using some terminology in this article, but I have a resource page available that break down each variable here:

http://www4.ncsu.edu/~jmlheure/index6.html

We have heard of the El Nino/La Nina cycle before, but we have different indices to measure the El Nino Southern Oscillation (will be called ENSO from here on out). In the image below are four samples of ENSO based indices: Nino 1+2, Nino 3, Nino 3.4, and Nino 4.

  The sector that is of most interest to us is Nino 3.4. Nino 3.4 has the most influence on transferring the anomalies caused by a weakened/reversed equatorial winds to the Southeast. Nino 1+2 would exhibit the greatest negative temperature anomaly for Florida, Nino 3 would have a greater effect on the Gulf Coast, Nino 3.4 would push the extent into the Southeast and Deep South, and Nino 4 would show the most anomalies for Texas and the Deep South. Conversely, positive temperature anomalies would span from the Great Lakes for Nino 1+2, to the upper Midwest for Nino 4.

Which, brings me to my first point. We are entering into a weak El Nino, but it's an EASTERLY based El Nino (Nino 1+2). I project that the El Nino will soon include Nino 3 but will remain near neutral to slightly weak El Nino for Nino 3.4 and Nino 4 for the early part of winter. That means that Florida and the Gulf Coast may see a very rainy, cool start right off the bat but otherwise we may have a slow start to this winter.

Our second long term variable, the Pacific Decadal Oscillation. We have been in a very negative PDO phase for the past year, and have been riding a negative PDO for the past 3 years (with the exception of the 2009-2010 winter, and we know how that one turned out).

Positive PDO temperature anomalies

PDO index (since the year 2000)

The PDO is trending positive, although very slowly. The most recent PDO index number for June was -0.87. For July it should be slightly greater since the Central Pacific Ocean's temperature anomalies have started to decrease in intensity. A + PDO allows for cooler weather to settle across the East Coast. A -PDO hurts our chances for cooler weather, since it indirectly promotes a more zonal flow entering into the Pacific Northwest. That killed us last winter. A +PDO indirectly promotes a storm track that digs farther south into the United States (and conversely, a storm track that pushes much farther north in the Pacific Basin).

We are likely to move towards a near neutral to a slightly +PDO this winter, although the setup is going very slowly and with a lag time between the PDO and influences farther downstream (United States), we are unlikely to see a beneficial weather pattern for cold/snow until later in the winter.

Conclusion: We will have a sluggish start to our winter, with both an easterly oriented El Nino and a slowly warming central Pacific Ocean. Remember that these are long term teleconnection patterns and the shorter term patterns will be our wild cards, making this sway either way (colder or warmer). Florida will have an unusually wet and cool start to the winter due to the strong subtropical jet influence. The PDO will not come into full play until mid winter, where we will see a cooling effect over the east coast. The snow track in early winter will be over the Ohio River Valley/Great Lakes and the split storm track will inhibit large scale snow storms. The storm track will become very active the second half of winter for the Mid-Atlantic. Cyclogenesis will be very prevalent in the Gulf of Mexico throughout winter but will be limited to smaller, weaker disturbances in the early part of winter due to the decoupled subtropical/polar jet stream. Cyclongenesis from an easterly based El Nino may carry storms away from the Atlantic Coast and preventing an interface with the polar jet. This would hurt our snow chances, especially with an already cold stratosphere giving us a stronger polar vortex. When the PDO starts to influence the polar jet in a positive manner, we will see larger systems start to track up the Mid-Atlantic coast. But for the first half of winter, we will see many storms simply track off the coast altogether, with the northern snow track being weak with numerous alberta clipper systems.

Verdict: Slow start to the winter, possibly cool/wet (limited snow), increasingly favorable conditions set us up for less frequent, but stronger synoptic storms the second half of winter, with better snow chances. Likely to be consistently cool (chilly) and wet. Storms are more likely to start tracking up the coast the second half of winter. Snow totals estimated to be near normal to slightly below normal, even with the El Nino setup (due to the decoupled subtropical/polar jet). A slow transition to more favorable central and equatorial Pacific conditions with an already cold stratosphere (strong polar vortex) may keep many storms from maturing early on. Deep South and the Ohio River Valley benefit from the easterly ENSO setup, due to a better chance of jet streams getting within close enough proximity to put a cold sector with the storm systems.

Vorticity correlation plots

To proceed to part II, click below:

http://lheureuxsweather.blogspot.com/2012/07/2012-2013-winter-prediction-part-ii.html